Method of manufacturing composite material

ABSTRACT

Disclosed is a method of manufacturing a composite sheet. The method comprises (a) irradiating a sheet of fibres and a matrix film at an irradiation zone with a plasma at substantially atmospheric pressure, and (b) impregnating the sheet of fibres with the matrix at an adhesion zone. The processes (a) and (b) are performed simultaneously, and the matrix film is irradiated with a plasma at said irradiation zone after being unwound from a roller and prior to entering said adhesion zone.

RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.12/375,108, filed Jan. 26, 2009 and is based on InternationalApplication Number PCT/GB2007/050462 filed Aug. 1 2007, and claimspriority from British Application Number 0615644.2 filed Aug. 7, 2006,the disclosures of which are hereby incorporated by reference herein intheir entirety.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus formanufacturing a composite material.

BACKGROUND OF THE INVENTION

In U.S. Pat. No. 5,108,780 a single fibre of reinforcing filament isirradiated with a plasma in a vacuum chamber prior to being coated witha thermoplastic coating. Immediate coating of the plasma treated fibrewith the thermoplastic produces stronger interfacial shear strength thanwhen the fibre is exposed to air or other free-radical-quenching speciesbefore it is coated.

The abstract of JP2005171432 describes a method of manufacturing fibresfor polymer composite reinforcement. The fibres are subjected to a firstplasma treatment under ordinary pressure followed by a second plasmatreatment in a medium containing a gaseous alkene or alkyne at ordinarypressure. An adhesive is imparted after the plasma treatments.

SUMMARY OF THE INVENTION

A first aspect of the invention provides a method of manufacturing acomposite sheet, the method comprising:

-   -   a. irradiating a sheet of fibres at an irradiation zone with a        plasma at substantially atmospheric pressure, and    -   b. impregnating the sheet of fibres with a matrix at an adhesion        zone;

wherein processes a. and b. are performed simultaneously.

The first aspect of the invention irradiates a sheet of fibres (insteadof a single fibre) and simultaneously runs an impregnation process toproduce a sheet of fibres impregnated with matrix (commonly known in theart as a “prepreg”). This can be contrasted with the prior art abovewhich only produces a single filament of fibre. The method enables asheet to be formed without having to treat the fibres with anintermediate product (for example the thermoplastic in U.S. Pat. No.5,108,780 or the alkene/alkyne in JP2005171432).

The sheet of fibres may be fully impregnated, or only partiallyimpregnated to form a so-called “partial prepreg”.

Irradiating at substantially atmospheric pressure means that no specialcontainment system is required for the irradiation zone.

Typically process b. is also performed at substantially atmosphericpressure, typically in air. This runs contrary to the teaching of U.S.Pat. No. 5,108,780 which requires coating of the fibre in a controlledenvironment (that is, either in a vacuum or an inert gas).

The sheet of fibres may be impregnated by application of a fluid matrixmelt, or the matrix may be in a sheet form during process b. Directapplication of a fluid matrix melt provides the advantage that a processstep (formation of the matrix sheet) can be omitted. However, the use ofa sheet of matrix is preferred because this requires less modificationof conventional manufacturing processes, enables the matrix to beirradiated more easily, and enables the preparation of a partialprepreg, if desired.

Preferably the sheet of fibres is moving during step a, and preferablythe sheet of fibres is moving during step b. This enhances the speed ofthe method, and ensures uniform irradiation.

Preferably the method further comprises moving the sheet of fibres fromthe irradiation zone to the adhesion zone in less than 30 seconds.

A second aspect of the invention provides apparatus for manufacturing acomposite prepreg, the apparatus comprising:

-   -   a plasma source for irradiating a sheet of fibres with a plasma        at substantially atmospheric pressure, and    -   means for impregnating the sheet of fibres with the matrix.

A third aspect of the invention provides a method of manufacturing acomposite material, the method comprising:

-   -   irradiating a matrix sheet with a plasma, and    -   coating a filler with the irradiated matrix sheet.

The third aspect of the invention recognises that irradiation of thematrix sheet may be used (optionally in conjunction with irradiation ofthe filler) to enhance adhesion between the filler and the matrix. Thefiller may be a sheet of fibres (in common with the first aspect of theinvention) or may be a non-fibrous material or a single fibre.

A fourth aspect of the invention provides apparatus for manufacturing acomposite material, the apparatus comprising:

-   -   a plasma source for irradiating a matrix sheet with a plasma,        and    -   means for coating a filler with the irradiated matrix sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theaccompanying drawings, in which:

FIG. 1 shows a first step in a method of manufacturing a compositeprepreg; and

FIG. 2 shows a second step in the method.

DETAILED DESCRIPTION OF EMBODIMENT(S)

Referring to FIG. 1, apparatus 1 for manufacturing a matrix film isshown. A coating head 2 comprises a funnel 3 filled with liquid matrixmaterial 4: either a “melt” or a dispersion. The opening of the funnel 3is positioned between a pair of rollers 5. The liquid matrix material 4is applied by the rollers 5 to the upper face of a sheet of releasepaper 6 which is fed continuously from a release paper roll 7. The sheetof matrix film 8 and release paper 6 are wound onto a roller 10. When aroll of desired size has been formed, the flow of matrix 4 from thecoating head is stopped, and the roller 10 is reversed. The matrix film8 is wound onto a roller via a guide roller 12 to form a roll 11 ofmatrix film. At the same time the release paper 6 is wound back onto therelease paper roll 7. The roll 11 is then removed and the process isrepeated to form a second roll 13 of matrix film shown in FIG. 2.

The matrix material 4 is typically a polymer, and may be thermosetting(for example epoxy resin) or thermoplastic (for examplepolyetheretherketone—PEEK).

Referring to FIG. 2, a sheet of fibres 20 is fed from a roller (notshown) via a pair of guide rollers 21,22. The fibres making up the sheet20 may be made of any organic or inorganic material such as carbon,glass, natural fibre or thermoplastic. The sheet 20 may be in the formof a unidirectional tape or a woven fabric. A pair of matrix films areunwound from the matrix film rolls 11,13 via rollers 22,23. Thethree-layer assembly is then heated by a heater 24 and compressedbetween three pairs of consolidation rollers 25. This causes the sheetto be impregnated with the matrix material to form a sheet of prepreg26. The prepreg 26 is shown in FIG. 2 as two layers, but in reality willeffectively be a single layer of matrix-impregnated fibre. The prepreg26 is then wound on to a roller 27 along with a layer of release paper28 which is unwound from a release paper roll 29 and applied to theprepreg by a pair of rollers 30,31.

Prior to entering an adhesion zone (indicated generally at 32, anddefined by the rollers 22,33, heater 24 and consolidation rollers 25)the fibre sheet 20 and/or the matrix films from rolls 11,13 areirradiated with plasma in an irradiation zone (indicated generally at33). Three plasma sources are shown in FIG. 2:

-   -   a first source 40 which is directed at the nip of the roller 22        so as to irradiate the opposed faces of the fibre sheet and the        lower matrix film;    -   a second source 41 which is directed at the nip of the roller 23        so as to irradiate the opposed faces of the fibre sheet and the        upper matrix film; and    -   a third source 42 which is directed at the upper matrix film        only.

Although three sources are shown in FIG. 2, more or less plasma sourcesmay be used as required. Thus in general, plasma sources may be used toirradiate the fibre sheet only; one or both of the matrix films only; orthe fibre sheet and one or both of the matrix films (as in FIG. 2).

Each plasma sources may be for example:

-   -   a “Plasmatec” plasma unit supplied by Plasmatec Inc. of        Montreal, Canada;    -   a “Tantec” plasma unit supplied by Dyne Technology Ltd, of        Tamworth, UK; or    -   an “AX Series” plasma unit supplied by Adtec Europe Ltd (UK) of        Hounslow Business Park, UK.

The plasma sources generate plasma at substantially atmosphericpressure. This means that the plasma sources do not need to be housed ina vacuum chamber as in U.S. Pat. No. 5,108,780, but instead may behoused under normal conditions (that is, in air at atmospheric pressure)along with the rest of the apparatus.

The irradiation and impregnation process are run simultaneously, insteadof being run in series as batch processes. This enables the fibre sheetto be impregnated quickly after irradiation, while the active freeradicals are still present.

The rollers are run continuously, so that the fibre sheet and matrixfilms are moving during irradiation and impregnation.

The plasma may be generated at ambient or elevated temperature and maybe any mixture of gases such as oxygen, argon and nitrogen mixed in anyproportion to form the required ionic species for treating the material.For example, the plasma may be:

-   -   nitrogen/argon    -   nitrogen/oxygen    -   nitrogen/oxygen/argon    -   air

Although only three plasma sources are shown in FIG. 2, depending on thewidth of the sheet 20, further plasma sources may be arranged in anarray (that is, out of the plane of FIG. 2) to irradiate the full widthof the fibre sheet and/or matrix films. The width may range between 3 mmand 20 metres.

The irradiation of the fibres and/or matrix generates free radicals ontheir surfaces and enhances adhesion between these components in theprepreg. These free radicals have a limited dwell time, so the plasmasources 40-42 are positioned sufficiently close to the rollers 22,23,and the rollers are run at a sufficient speed, to ensure that the layersare brought together by the rollers 22,23 as soon as possible afterirradiation, typically less than 30 seconds after irradiation andpreferably less than one second after irradiation. Typically the processis run at 2-10 metres per minute, although speeds of up to 400 metresper minute may be possible.

No separate adhesive is applied to the fibre sheet prior to combinationwith the matrix.

The prepreg can be used in the formation of aircraft components such aswing skins, stringers, spars, wing access panels, or spoilers; ornon-aircraft components such as bicycle frames, industrial goods, sportsgoods, automotive products, wind energy products, or marine productssuch as boat hulls.

Although the invention has been described above with reference to one ormore preferred embodiments, it will be appreciated that various changesor modifications may be made without departing from the scope of theinvention as defined in the appended claims.

1-20. (canceled)
 21. A method of manufacturing a composite sheet, themethod comprising: a. irradiating a sheet of fibres and a matrix film atan irradiation zone with a plasma at substantially atmospheric pressurefrom a plasma source, and b. impregnating the sheet of fibres with saidmatrix film at an adhesion zone; wherein processes a. and b. areperformed simultaneously, said matrix film is unwound from a matrix filmroll via a roller, opposed faces of said sheet of fibres and said matrixfilm are brought together at a nip of said roller, and said sheet offibres and said matrix film are irradiated by directing said plasmasource at said nip of said roller so as to irradiate said opposed facesof said sheet of fibres and said matrix film.
 22. The method of claim 21wherein process b. is performed at substantially atmospheric pressure.23. The method of claim 21 wherein process b. is performed in air. 24.The method of claim 21 further comprising moving the sheet of fibres andthe matrix film from the irradiation zone to the adhesion zone in lessthan 30 seconds.
 25. A method of manufacturing a composite sheet, themethod comprising: a. irradiating a sheet of fibres and a first matrixfilm at a first irradiation zone with a plasma at substantiallyatmospheric pressure from a first plasma source, and b. impregnatingsaid sheet of fibres with said matrix film at an adhesion zone; whereinprocesses a. and b. are performed simultaneously, said first matrix filmis unwound from a first matrix film roll via a first roller, opposedfaces of said sheet of fibres and said first matrix film are broughttogether at a nip of said first roller, and said sheet of fibres andsaid first matrix film are irradiated by directing said first plasmasource at said nip of said first roller so as to irradiate said opposedfaces of said sheet of fibres and said first matrix film, and whereinthe method further comprises: c. irradiating said sheet of fibres and asecond matrix film at a second irradiation zone with a plasma atsubstantially atmospheric pressure from a second plasma source, and d.impregnating the sheet of fibres with said second matrix film at saidadhesion zone; wherein processes c. and d. are performed simultaneously,said second matrix film is unwound from a second matrix film roll via asecond roller, opposed faces of said sheet of fibres and said secondmatrix film are brought together at a nip of said second roller, andsaid sheet of fibres and said second matrix film are irradiated bydirecting said second plasma source at said nip of said second roller soas to irradiate said opposed faces of said sheet of fibres and saidsecond matrix film.
 26. The method of claim 25 wherein process b. isperformed at substantially atmospheric pressure.
 27. The method of claim25 wherein process b. is performed in air.
 28. The method of claim 25further comprising moving the first and second matrix films from thefirst and second irradiation zones to the adhesion zone in less than 30seconds.
 29. Apparatus for manufacturing a composite sheet, theapparatus comprising: a. a plasma source for irradiating a sheet offibres and a matrix film with a plasma at substantially atmosphericpressure, b. means for impregnating the sheet of fibres with the matrixfilm; and c. a roller for bringing together opposed faces of said sheetof fibres and said matrix film at a nip of said roller, wherein saidplasma source is directed at said nip of said roller so as to irradiatesaid opposed faces of said sheet of fibres and said matrix film.
 30. Theapparatus of claim 29 further comprising a matrix film roll, whereinsaid matrix film is unwound from said matrix film roll via said roller.31. The apparatus of claim 29 further comprising: a second plasma sourcefor irradiating said sheet of fibres and a second matrix film with aplasma at substantially atmospheric pressure, means for impregnatingsaid sheet of fibres with said second matrix film; and a second rollerfor bringing together opposed faces of said sheet of fibres and saidsecond matrix film at a nip of said second roller, wherein said secondplasma source is directed at said nip of said second roller so as toirradiate said opposed faces of said sheet of fibres and said secondmatrix film.